Exercise Behavior Among Young Adults Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Exercise Behavior Among Young Adults Study (NCT02204176), a randomized na study. The primary outcome is Total Physical Activity.

2. Clinical Question

3. Trial Design

The Exercise Behavior Among Young Adults Study was a completed randomized, parallel-group study sponsored by Wayne State University. The registry lists enrollment of 221 and classifies the study phase as not applicable. Masking was none, so the study is described as unmasked. The dates recorded for the study are 2013-08 for start and 2016-05 for primary completion.

Participants were assigned to exercise information, action planning, or realistic-effort action planning. The study description frames these as three approaches for college students. The information-only approach covered types and benefits of exercise; action planning added training on creating specific intentions to support exercise initiation; and realistic-effort action planning added a personality-informed component linked to learned industriousness. The registry record does not report details of sequence generation, allocation concealment, or the exact assignment procedure.

The primary outcome was total physical activity, assessed 2–3 months after the initial intervention session. The posted group summaries include 74 participants for exercise information, 73 for action planning, and 74 for realistic-effort action planning. These outcome counts do not by themselves describe participant flow from randomization through follow-up. A flow account, reasons for missing outcome data, and the populations included in the analyses are not reported in the registry record.

The registry lists six outcome measures, but reports no analyses in its analyses listing. The available arm summaries and comparisons therefore need to be read as posted descriptive results and simple unadjusted recalculations, rather than as a documented account of a prespecified sponsor analysis. The original statistical analysis plan and the study's own sample-size justification are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Total Physical Activity, measured over 2-3 months after initial intervention session.

The primary endpoint is total physical activity, expressed in total metabolic equivalent units. It is based on the Godin Leisure-Time Exercise Questionnaire, which asks about the frequency of typical weekly strenuous, moderate, and mild exercise in an open-ended format. Reported frequencies are weighted by the corresponding metabolic equivalents and summed to form a total score. Higher scores indicate more exercise engagement. The assessment timeframe is 2–3 months after the initial intervention session.

This measure offers a summary of reported activity across different levels of exercise intensity. Combining the activity categories into one score allows the study to compare average overall activity between the training approaches, rather than considering only one intensity category. The reported endpoint is a continuous measure, so its arm-level summaries are means with standard errors, and the comparisons are expressed as mean differences.

The registry also says participants were loaned pedometers to obtain objective activity measures. The description explains that the devices could record steps and store information, but it does not report a separate pedometer result for the primary endpoint. The posted primary outcome is described through the questionnaire-derived total score; whether pedometer data were analyzed or used in another outcome is not reported in the registry record.

7. Results Posted in the Registry

• Action Planning: mean 37.80 versus 34.21 on control; difference 3.59 (95% CI -3.89 to 11.07), standardized effect d = 0.16; z-test p = 0.347.
• Realistic Effort Action Planning: mean 39.42 versus 34.21 on control; difference 5.21 (95% CI -2.17 to 12.59), standardized effect d = 0.23; z-test p = 0.166.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Exercise Self-efficacy

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Action Planning: mean 3.05 versus 2.92 on control; difference 0.13 (95% CI -0.15 to 0.41), standardized effect d = 0.15; z-test p = 0.360.
  • Realistic Effort Action Planning: mean 3.09 versus 2.92 on control; difference 0.17 (95% CI -0.09 to 0.43), standardized effect d = 0.21; z-test p = 0.206.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Action Planning and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Realistic Effort Action Planning and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary outcome is exercise self-efficacy, assessed at the same 2–3 months after the initial intervention session. Its group means follow the same broad directional pattern as the primary endpoint: both planning groups have higher posted averages than exercise information. The comparison intervals include zero, and the unadjusted p-values do not clearly distinguish the groups. This gives a generally similar, but uncertain, pattern across self-efficacy and total physical activity.

That similarity may be useful as context, but it does not independently confirm the primary finding. Self-efficacy and reported exercise behavior are different measures, and a parallel direction across them does not establish that a change in one produced a change in the other. The registry does not report a mediation analysis, an adjusted analysis, or a prespecified relationship between these outcomes.

The secondary results also require caution because the registry record does not report how many outcomes or comparisons were planned for formal testing, nor how multiplicity was handled. When several outcomes or contrasts are examined, unadjusted results can make chance patterns more likely across the full set of analyses. This is a general statistical concern; it does not show that the observed results are false. It means that secondary results without a reported multiplicity plan should carry less weight than a clearly prespecified primary analysis.

The registry lists six outcome measures, while secondary results are posted for exercise self-efficacy. It does not report analyses for the other listed measures. The available secondary evidence is therefore limited in scope. Taken together, the secondary pattern is directionally compatible with the primary summaries, but it remains imprecise and should be treated as supportive context rather than a separate definitive conclusion.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Exercise Self-efficacy
• Exercise Self-efficacy

9. Statistical Interpretation

10. Statistical Methods Explained

Outcome scale and summaries. Total physical activity is treated as a continuous measure. The registry reports an arm mean and its standard error for each group. A mean describes the central average of the observed scores; the standard error describes the uncertainty in estimating that average from the participants whose results are included. A standard error is not the spread of individual participants' scores. The registry does not give the standard deviation of the endpoint directly in the arm summaries.

Mean differences. The comparisons express the average in a planning group minus the average in the exercise-information group. A positive estimate means the posted average is higher in the planning group; a negative estimate would mean it is lower. For action planning, the unadjusted recalculated difference is 3.59. For realistic-effort action planning, it is 5.21. These are simple unadjusted recalculations from posted summary statistics, rather than documented adjusted sponsor estimates. The registry record does not report a sponsor analysis for these comparisons.

Confidence intervals. A confidence interval gives a range of values compatible with the observed data under the calculation and its assumptions. It conveys precision as well as the direction and size of an estimate. The primary comparison intervals extend across zero, so the summaries do not distinguish clearly between a positive difference, no average difference, and a negative difference. A confidence interval is not a guarantee that the true value lies in the reported range, and it does not describe the range of individual outcomes.

Unadjusted p-values. The posted p-values for the primary comparisons are unadjusted. In general, a p-value evaluates how unusual data at least as incompatible with a specified null model would be if that model were true, given the statistical procedure. It is not the probability that the null hypothesis is true, the probability that a result occurred by chance, or a measure of clinical importance. Because the registry does not report a multiplicity plan, these p-values should be considered in the context of the two comparisons and the other outcomes, not as standalone proof.

Standard errors and uncertainty. The arm-level standard errors are 2.59 for exercise information, 2.8 for action planning, and 2.73 for realistic-effort action planning. The comparison calculations also report pooled standard deviations, which are 23.11 for action planning versus exercise information and 22.89 for realistic-effort action planning versus exercise information. A standard deviation describes variation among individual observations; a standard error describes uncertainty in an estimated mean. The two serve different purposes. When individual scores vary substantially relative to a mean difference, the estimate may be imprecise unless there are enough observations to estimate the difference well.

What the calculations do not establish. The reported recalculations are unadjusted and based on summary statistics. They do not account for any covariates, clustering, departures from model assumptions, or missing-data procedures unless those are reflected in the posted summaries; such methods are not reported in the registry record. The registry also does not report diagnostics, an analysis population definition, or a protocol for handling multiple comparisons. These omissions limit how fully the statistical analysis can be evaluated.

General statistical context. Random assignment is generally intended to make comparison groups similar on average at the start of a study, but the registry record does not provide enough information to assess implementation of the assignment process or baseline balance. In general, an unmasked design can permit expectations or knowledge of assignment to influence behavior, reporting, or assessment. That is a design consideration, not proof that bias occurred in this study. For a self-reported activity measure, how participants report their behavior is especially relevant to interpretation, but the registry does not describe any validation or blinding procedures.

Over-dispersion is a general concern when outcomes vary more than a statistical model assumes. It is particularly relevant to count outcomes or some event-rate analyses, and can make model-based standard errors too small if ignored. The primary outcome is reported as a continuous score, and the registry does not report an over-dispersion assessment. It would therefore be inappropriate to claim that over-dispersion was present or that a particular adjustment was used.

11. Confidence Intervals and Precision

The primary estimates are positive, but their confidence intervals are wide enough to include zero. For action planning, the estimate is 3.59 and the 95% confidence interval is -3.886 to 11.07. For realistic-effort action planning, the estimate is 5.21 and the 95% confidence interval is -2.166 to 12.59. Each interval includes values consistent with a lower average in the planning group, no average difference, and a higher average. The posted summaries therefore do not pin down the direction or magnitude with high precision.

The interval width matters because a point estimate alone can make an uncertain result appear more definite than it is. Here, the estimated average differences are small relative to the ranges of values compatible with the calculations. The arm-level standard errors, 2.59, 2.8, and 2.73, also indicate uncertainty around the respective means, although they are not themselves intervals for the between-group differences.

Confidence intervals quantify uncertainty under the statistical procedure; they do not capture every source of uncertainty. They do not address possible selection effects, differences in reporting, missing data, or limitations in outcome measurement. The registry record does not report enough detail to assess those issues fully. The intervals should therefore be interpreted as precision measures for the posted unadjusted comparisons, not as a complete description of all uncertainty about the study.

The interval endpoints and p-values are consistent with results that do not sharply separate the groups under the unadjusted comparisons. This does not establish equivalence, and it does not show that any difference is too small to matter. The registry record does not provide a threshold for a meaningful difference. A more precise estimate would be needed to narrow the plausible range of average effects.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size planning figures are participants per arm, not a total across groups. The event-count convention for time-to-event outcomes does not apply to this continuous physical-activity outcome. The registry lists planning assumptions of a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect. These are planning illustrations based on the observed effect, not the original design assumptions; the trial's own sample-size justification is not reported in the registry record.

The 80% power column gives the number of participants per arm estimated to yield an 80% chance of detecting the specified effect under the planning assumptions, if that effect and the model assumptions were correct. The 90% power column uses a higher target chance of detection and consequently requires more participants per arm for the same effect. These are prospective planning quantities: they describe hypothetical designs, not the achieved power of the completed study.

Rows for 100%, 75%, and 50% of the observed effect illustrate how the planning requirement changes when the target effect is smaller than the observed estimate. Smaller effects need more participants because they are harder to distinguish from random variation. The calculations use the observed effect as an input, which is uncertain; they are not a guarantee that a future study with the indicated size would detect an effect.

For example, the primary comparison planning figures are reported separately for each planning approach and each target effect fraction. Their interpretation depends on the assumed equal allocation and normal approximation. The registry record does not report whether the original trial used these assumptions or a different sample-size calculation. The figures are planning illustrations only, not observed power.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 3.590; pooled standard deviation σ = 23.111.
2. n = 2 × (1.96 + 0.842)² × 23.111² / 3.590² = 650.5, rounded up to 651 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 3.59                      # observed difference in means
sigma <- 23.1105582976177                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2204176)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 651 (80% power), 871 (90% power)
 75% of observed effect: n per arm = 1,157 (80% power), 1,549 (90% power)
 50% of observed effect: n per arm = 2,603 (80% power), 3,484 (90% power)
power.t.test: 651.5 
Simulated power at n = 651 per arm: 0.803 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry record does not report a statistical analysis plan, a hierarchy of outcomes, or a method for controlling multiplicity. It lists six outcome measures and gives two comparisons against exercise information for the posted primary outcome, alongside secondary outcome information. When multiple outcomes or comparisons are considered, the chance of at least one apparently notable result can increase. Adjustments or a prespecified hierarchy can address this concern, but whether either was used is not reported in the registry record.

Missing-data handling is also not reported. The posted primary summaries include 74 participants in exercise information, 73 in action planning, and 74 in realistic-effort action planning. These counts describe the reported outcome summaries but do not explain whether all randomized participants contributed data, why any data may be absent, or how missing outcomes were treated. The registry does not report an intention-to-treat definition, a per-protocol population, imputation, or sensitivity analyses.

The registry record does not describe baseline comparisons, adjustment for covariates, or the statistical model used by the sponsor. Its analyses listing reports no analyses. Accordingly, the displayed mean differences and p-values are best understood as unadjusted recalculations from posted summary statistics, not as a substitute for an undocumented sponsor analysis. The registry also does not report whether the outcome assessors or data analysts were masked; the study-level masking entry is none.

These reporting gaps do not demonstrate that the study mishandled multiplicity or missing data. They limit the ability to judge whether the reported estimates represent the intended analysis and how robust they are to alternative assumptions. A fuller assessment would require information about the original analysis plan, participant flow, outcome availability, analysis populations, and prespecified handling of multiple comparisons; these details are not reported in the registry record.

15. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry lists zero serious adverse events, zero other adverse events, and zero deaths in each of the three groups. For each listed group, the registry also gives 221 participants at risk for serious and other adverse events. These at-risk figures are recorded identically across groups, even though the primary outcome summaries have different group counts. The safety figures should therefore be read as recorded in the registry, not as a clear account of group-specific safety denominators.

Zero reported events means that the registry lists no affected participants for these categories; it does not establish that no events occurred outside the recorded definitions or reporting process. The registry does not provide event descriptions, ascertainment procedures, follow-up duration for safety, or an explanation of the repeated at-risk counts. No serious-event terms are listed. These data describe the safety reporting in the registry record and should not be used to infer more than that.

16. What the Result Does, and Does Not, Mean

The posted primary summaries show higher average total physical-activity scores in the two planning groups than in the exercise-information group at 2–3 months after the initial intervention session. The unadjusted recalculated differences are positive, but both confidence intervals include zero. The estimates are therefore uncertain: the data do not precisely establish the size or direction of an average difference between either planning approach and exercise information.

This is not evidence that the approaches work, and it is not evidence that they do not work. A result that does not clearly distinguish groups is not the same as proof that the groups are equivalent. The registry does not report a threshold for a meaningful difference, and the intervals span values on both sides of zero. The available summaries cannot settle whether any difference would matter in practice.

The comparisons are each against exercise information. They do not directly answer whether realistic-effort action planning differs from action planning. The study description identifies a layered set of approaches, but the posted comparisons do not establish which component, if any, accounts for the observed pattern. The registry record does not report a component-specific analysis.

The endpoint is a questionnaire-derived score of reported exercise, and the follow-up is limited to 2–3 months after the initial session. Although pedometers were loaned, separate pedometer findings are not reported in the registry record. The result cannot be extended to longer-term activity, other populations, or objective step counts on the basis of the posted information alone. The study was conducted among college students, but detailed participant characteristics are not reported in the registry record.

The most defensible reading is that the observed group averages lean toward higher activity scores for the planning approaches, with substantial uncertainty and important reporting limitations. The results are descriptive and do not by themselves establish a causal or clinically meaningful effect.

17. Why This Trial Matters Statistically

This study is statistically instructive because it separates a point estimate from its precision. The primary mean differences are positive, but the confidence intervals cross zero and cover a range of plausible values in both directions. Looking only at which group has the higher observed mean would miss the uncertainty in the comparison. Looking only at an unadjusted p-value would also miss the range and scale of values compatible with the data.

The study also illustrates why outcome definition matters. Total physical activity is a continuous score built from reported frequency across exercise intensities. That summary is not interchangeable with step counts or with a direct measure of long-term activity. The registry mentions pedometers, but does not report separate pedometer results, so the interpretation must stay tied to the posted questionnaire-based endpoint.

Another useful lesson is the distinction between a planning calculation and a trial's original design justification. The registry includes sample-size planning illustrations based on observed effects, but does not report the original design assumptions. Those illustrations can help readers understand how target effect size and desired power affect planning; they cannot explain whether the completed study was adequately designed for its stated question.

Finally, the record shows how incomplete analysis reporting affects interpretation. The absence of reported analysis details does not prove that appropriate methods were not used, but it prevents readers from evaluating multiplicity, missing data, analysis populations, and model choices. Clear reporting of those decisions is essential for understanding what an estimate represents and how confidently it can be interpreted.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several limitations specific to this study constrain interpretation. The outcome summaries are available for a follow-up 2–3 months after the initial intervention session, but the registry record does not report later follow-up results. The evidence therefore addresses only the stated follow-up, not whether any pattern persisted.

The primary endpoint is based on self-reported exercise frequency in an open-ended questionnaire. Such a measure captures reported behavior, not necessarily objectively recorded activity. The registry says participants were loaned pedometers, but does not report separate pedometer results or explain how the device data were used. That leaves unclear whether the objective measurements informed any posted analysis.

The study is described as unmasked, and the outcome includes participant reports. This combination is relevant because expectations could influence reporting or behavior in general, although the registry record does not establish that such influence occurred. It also does not report details about allocation concealment, baseline balance, adherence to the training sessions, or contamination between approaches.

Participant characteristics and eligibility criteria are not reported in the registry record beyond the description of college students and young adults. This limits assessment of how well the results apply to other groups. The registry also does not describe missing-data procedures, analysis populations, or whether all randomized participants were included in the outcome summaries. The primary group counts are reported, but a participant-flow account is not.

Finally, no sponsor analysis is listed, and the registry does not report the original sample-size justification, a formal analysis plan, or multiplicity handling. The posted comparisons are unadjusted recalculations, with intervals that include zero. Together, these design and reporting limits make the results useful as a description of the posted summaries, but insufficient for a firm conclusion about the effects of the training approaches.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Exercise Behavior Among Young Adults Study — NCT02204176.
• Registry record last updated 2019-05-03; status last verified 2019-04.
• Results first posted 2019-05-03.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT02204176 is a completed randomized, parallel-group study of exercise behavior among college students. It compared exercise information with action planning and realistic-effort action planning. The primary outcome was questionnaire-derived total physical activity, assessed 2–3 months after the initial intervention session.

The posted group means were higher in both planning groups than in the exercise-information group, but the unadjusted recalculated mean-difference confidence intervals included zero. The registry record does not report a sponsor analysis, the original sample-size justification, or key details on missing data and multiplicity. The results are therefore best read as uncertain comparisons of the posted summaries, not as definitive evidence for or against an approach.